2Introduction Superheaters and Reheaters Corrosion and Erosion Problems Benefits of Chromium in Ni-Base MaterialsFiller Metal 72: High Chromium and WeldableCorrosion ExamplesApplication SuccessesThis is what will we cover in this presentation.
3Corrosion Test Simulating Low-NOx Corrosion Conditions The test environment consisted of the following gas mixtures at 1000°F:Reducing Cycle: N2-16%CO2-10%H2O-5%CO-2%H2S (flow rate 500 sccm).Oxidizing Cycle: N2-17.2%CO %H2O (CO and H2S turned off).
4Corrosion Test Simulating Low-NOx Corrosion Conditions The test consisted of alternating cycles consisting of 4 days reducing and 3 days oxidizing.The test was conducted in a horizontal electrically heated muffle furnace having a 100mm diameter mullite tube with sealed end caps and a sealed pushrod mechanism for inserting and removing samples to and from the hot zone.Samples were cycled to room temperature and weighed at 500h, 1000h, 3000h and 4940h.
5Inlet and Calculated Equilibrium Outlet Compositions for Laboratory Simulation of Low-NOx Boiler Environment at 1000°F
6Corrosion Test Simulating Low-NOx Corrosion Conditions Wrought samples for alloy 625 were produced from cold-rolled and annealed sheet. The machined test samples measured ~3mm X 10mm X 20mm.Wrought samples of alloys 622 and filler metal 72 were produced from hot-rolled and solution annealed wire rod; machined test samples measured ~6mm diameter X 20mm.Weld overlay samples of filler metals 53MD and 72 were fabricated by first applying two layers of overlay onto carbon steel using the p-GMAW process followed by removal of the top layer and machining samples. The machined test sample size was ~3mm X 10mm X 20mm.
7Mass change results after exposure at 1000°F (538°C) Under the Described Simulated Low-NOx Test Conditions
8Reducing to Neutral Atmosphere Low Grade CoalsSulfatesH2SThes were taken from the same tube from the DOE-McDonald study. Overlay was done with Save25. We’re not picking on Save 25, they were just a great example of poor performance.Cross Section of Superheater tube .250 inches per year wastage. (Save 25)Actual Tube Cut out - Facing Gas Flow
9Cross Section of Superheater Tubes from DOE – McDonald Study
10Numbering of Specimens Within Test Loop Exposed in a Subcritical Coal Fired Boiler Firing 3-3.5% Sulfur Ohio Coal
11Identification key for INCONEL weld overlays and alloys
12Wastage as a Function of Time for Superheater tube Materials
13Metal Loss As a Function of Position in Test Loop Exposed for 21,200 Hours in Coal Fired Boiler Firing 3-3.5% Sulfur Ohio Coal - Results Reported by McDonald
14Wastage rate of samples exposed to 560-650°C for 21,200 Hours
15Dependence of Corrosion Behavior in Synthetic Coal Ash/flue Gas Corrosion Upon Temperature - AusteniticsReference: M. Tamura, N. Yamanouchi, M Tanimura, S. Murase, "Promising Alloys for theHeat Exchangers of Advanced Coal Fired Boilers," Proceedings : Exposition and Symposium on Industrial Heat Exchanger Technology (Materials Park, Ohio: ASM International 1985), p. 273.Gas composition = 1%SO2-5% O2-15%CO2-Bal. N2Synthetic ash = 34%Na2SO441%K2SO4-25%Fe2O3
16Dependence of Corrosion Behavior in Synthetic Coal Ash/flue Gas Corrosion Upon Temperature - FerriticsReference: H. Teranishi, et al, presented at the International Conference on HighTemperature Alloys, Preprint Paper No. 21, Petten, The Netherlands, Oct 15-17,
18Cross Section Loss (Depth of Attack) for High Temperature Alloys Exposed at 700°C in Laboratory Flue Gases (1% SO2)Baker and SmithBlough and Stanko: N2-14%CO2-10%H2O-3.6%O2-1%SO2, 10% alkali sulfatesCastello, et al: N2-15%CO2-3.5%O2 -1%SO2, 10% alkali sulfatesBaker and Smith: N2-15%CO2-4%O2 -1%SO2, 5% alkali sulfates
19Cross Section Loss (Depth of Attack) for High Temperature Alloys Exposed at 700°C in Laboratory Flue Gases (0.25% SO2)Blough and Stanko: N2-14%CO2-10%H2O-3.6%O2-0.25%SO2, , 10% alkali sulfatesCastello, et al.: N2-15%CO2-3.5%O %SO2, 10% alkali sulfatesBaker and Smith: N2-15%CO2-3.5%O %SO2, 10% alkali sulfatesBaker and Smith
22FILLER METAL 72 FILLER METAL 72 Minimum Tensile Strength: 106,000 psi Yield Strength (0.2% offset): ,000 psiElongation %AWS A5.14, ERNiCr-4ASME IX, F-No. 43ASME II, SFA-5.14, ERNiCr-4ISO S.Ni6072Europe NiCr44TiUNS N06072Available for GMAW or GTAW welding.
23FILLER METAL 72 Super heater tube removed after in service testing. Reheater tuber overlaid with Filler Metal 72 after 2+ years of service at 1000 – 1100oF after simulated repair weld and LP inspection
24FILLER METAL 72 Hardness Profile after 2+ Years at 1000°F-1100°F
31Sample Reheater Tube Removed from Low Nox Boiler Actual Service – 6 years
32Field Success Philadelphia Electric Company - 671 Clad Reheater Tubes 9 years of service1100o F (595o C)Ave. 2.44% sulfur contentAve. 10.8% ash content671 unaffected by corrosion
33Field Success The Outlet Leg of a Secondary Superheater. 5 ½ years of service1000ºF (538°C) SteamCyclone coal fired 4.5-5% sulfur, 20% ashNo visible evidence of corrosion
34Field Success 1974 – 1980 trouble free service The UK Central Electricity Generating Board1974 – 1980 trouble free serviceTesting led to full replacement of reheater tubeStainless tubes had corroded at 3.5 mm/year
35Field Success Large Mid-West Power Provider Met 20 year design life Installed Muskingum River OH and Kammer, W.V.
36Field SuccessFuel-Ash Corrosion-Resistance in Power Plant Steam Superheaters.Operating temperature 1055ºF32 months and 66 monthsHigh sulfur pulverized coal671 Cladding remained uniform and showed minimal corrosion
37Filler Metal 72 Overlay on Superheater Tubes Overlaid SA213-T2 Superheater tubes installed in Rockport Unit I, Spring of 1999.
38Filler Metal 72 Overlay on Superheater Tubes Overlaid SA213-T2 Superheater tubes installed in Rockport Unit I, Spring of 1999.
39Filler Metal 72 Overlay on Superheater Tubes Overlaid SA213-T2 Superheater tubes installed in Rockport Unit I, Spring of 1999.
40Filler Metal 72 Overlay on Superheater Tubes Overlaid SA213-T2 Superheater tubes installed in AEP Rockport Unit I, Spring of 1999.
41Unifuse 360 overlay job using Spiral GMAW Followed by a GTAW pass welding process todeposit a corrosion resistant weld overlay usingAlloy 72 filler metalTubes were manufactured for use as Reheater Tubing in a coal-fired supercritical boiler- Base material was SA 213 Tp 304H 2.5” OD x 0.165” mwt.- Overlay thickness average is 0.070”- Typical Chemical Analysis:Ni 52.5%Cr 41.0%Fe 6.0%Ti 0.5%
42TESTING and RESULTS- Longitudinal and transverse cross-sections were cut from 5% of production (approximately 110 tubes)- Liquid Penetrant, X-Ray Flouresence and thickness measurements were made on the 5% samples and randomly on the balance of the production- None of the tests conducted revealed the presence of cracking or any major welding discontinuities. Additional to our test plan the customer performed extensive macrographic work on each of the sectioned samples (110 samples) with no evidence of defects when examined at 5X magnification.
47Summary Superheaters and Reheaters - Aggressive Corrosion/Erosion Conditions.- High Chromium Content Required to Resist Molten SulfateCorrosion.- Enhancement in Strength and Hardness Resulting fromExposure may Serve to Enhance Erosion Resistance.- Filler Metal 72 Weld Overlay Proven in the Laboratory and inthe Field to Possess Superior Corrosion Resistance.- Long-Term Experience with 671 Clad Tubes ReinforcesConfidence in Filler Metal 72.